1. Field of the Invention
The present invention relates to vehicle motion control devices and methods, and, in particular, to devices and methods for controlling the motion of a vehicle through controlling the distribution ratio of the driving force based on the forces that act on the wheels.
2. Description of the Related Art
Conventionally, there are known technologies for controlling the state of motion of a vehicle through controlling the distribution ratio of the driving force between the front and rear wheels and/or between the left and right wheels.
The main objective of these technologies is to improve steering by controlling the driving force distribution ratio to achieve an appropriate state of motion of the vehicle under certain driving conditions such as cornering. Japanese Patent Publication 3132190 disclosed a device for controlling the state of motion of a vehicle by means of a wheel frictional force utilization ratio. In the device, the wheel frictional force utilization ratios are calculated for the respective wheels, which are then controlled so that the wheel frictional force utilization ratios become close to the respective target values.
Japanese Kokai Laid-open Publication H 11-102499 disclosed a method wherein the state of motion of a vehicle is controlled by utilizing the fact that the vehicle behavior is affected by the elements in the system matrix of equations of state that describe the state of motion of the vehicle.
However, the main focus of the technologies described above is the effective utilization of the driving force; thus, issues such as stability and response are not fully considered. In particular, if the wheel friction utilization ratio is controlled to the limit during spinning, the control mechanism would rely heavily on the grip of the tires on the outer wheels, leading to problems such as the loss of stability against disturbances due to, for example, a sudden change in the friction coefficient with the road surface.
In other words, in the technologies described above, the nonlinear elements of the vehicle motion are not properly taken into consideration in controlling the vehicle behavior; as a result, there is a possibility that steering stability gets degraded.
The entire disclosures of Japanese Patent Publication 3132190 and Japanese Kokai Laid-open Publication H 11-102499 are incorporated herein by reference.